Carbon particulate monitor with preseparator

ABSTRACT

Carbon particulate concentration of diesel exhaust or other sampled gas is measured by collecting the particulate on a high efficiency filter while measuring the amount of sampled gas passing through the filter. The filtered particulate is then heated in an oxygen rich environment to oxidize carbon within the particulate to carbon dioxide. The amount of resulting carbon dioxide is measured with a closed measurement loop to derive a corresponding measurement of the amount of filtered particulate. Particulate concentration is calculated by comparing the amount of carbon particulate with the measured amount of sampled gas passed through the filter. Filtered particulate can be heated incrementally to obtain a measurement of volatile carbon components within the particulate prior to the oxidation of the non-volatile carbon component. The filter employed to collect the carbon particulate is of a high temperature resistant type making it reusable and can be either integral with or inserted into the oxidation chamber of the instrument. Oxidation of the particulate inherently concurrently cleans the filter for reuse. An upstream preseparator can extend the life of the high efficiency filter. Particulate can also be collected for analysis by using an accelerating impaction nozzle in conjunction with a heatable impaction plate.

This application is a division of application Ser. No. 07/877,542, filedMay 1, 1992, now U.S. Pat. No. 5,196,170 which is a continuation-in-partof application Ser. No. 07/612,562, filed Nov. 13, 1990, now U.S. Pat.No. 5,110,747.

BACKGROUND OF THE INVENTION

The present invention relates generally to measurement of carbonparticulates, and more particularly to a method and apparatus fordetermining the particulate level or concentration of a sampled gas,e.g. diesel exhaust.

The quality of air has become an important environmental concern withinrecent years. In an effort to curb air pollution and maintain airquality, strict vehicle exhaust emission guidelines have been set byfederal and state authorities. Requirements for diesel emissions areextremely stringent because of the harmful effects of diesel exhaustswithin the atmosphere. Therefore, each diesel vehicle sold, for examplewithin the United States, must pass certain emission tests and meetstrict environmental emission standards. To determine if emissionstandards have been met, it is necessary to measure the particulateconcentration of diesel exhaust. In order to accurately determinewhether a diesel engine meets emission standards, a reliable reading ofthe particulate concentration of diesel exhaust is necessary. Aninaccurate reading of diesel particulate concentration could result in adiesel engine improperly passing or failing emission tests. It is,therefore, desirable to utilize a technique for accurately and reliablymeasuring the particulate concentration of diesel exhaust.

Presently, diesel particulate is measured using a few different types ofsystems. One particular technique involves a direct measurement of themass of particulate within exhaust on a real-time basis. With thistechnique a tapered element oscillating microbalance such as that shownin U.S. Pat. No. 4,391,338 is capable of measuring the mass ofparticulate deposited on a filter. This technique is not inexpensive andgenerally requires a dilution tunnel for proper use. Another techniquefor measuring the amount of particulate concentration of diesel exhaustinvolves optical measurements. This technique, however, suffers from alack of accuracy and does not provide consistently reliable measurementsof particulate mass. Another technique for measuring the particulateconcentration of diesel exhaust involves forcing a measured amount ofexhaust through a filter which collects the particulate therein, andthen weighing the filter. The filter is preconditioned and preweighed sothat the difference in weight of the filter before and after its use isrepresentative of the amount of particulate within the exhaust. Thedisadvantage with this particular system is that it is extremely timeconsuming and labor intensive. Furthermore, the filter is not reusableafter each measurement cycle thereby making it necessary to obtain a newfilter for each diesel particulate measurement.

It is therefore an object of the present invention to provide atechnique to accurately measure the particulate concentration of dieselexhaust.

It is also an object of the present invention to provide a technique formeasuring the particulate concentration of diesel exhaust which is notlabor intensive or time consuming.

It is also an object of the present invention to provide a technique formeasuring the particulate concentration of diesel exhaust which utilizesa reusable filter or particulate collector to avoid the necessity ofdisposing of filters or collectors after they have been used to collectparticulate.

It is also an object of the present invention to provide a technique formeasuring the particulate concentration of diesel exhaust which providesconsistently reliable readings.

It is also an object of the present invention to provide a technique tomeasure the concentration of non-volatile diesel particulate and/orvolatile diesel particulate.

It is a further object of the present invention to provide a techniquefor measuring the carbon particulate level or concentration not only ofdiesel exhaust but also of other gaseous mixtures and samples.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and the objects of thepresent invention are achieved, by utilizing a technique for measuringcarbon particulate concentration of diesel exhaust or other sampled gasin accordance with the present invention. The invention involves amethod for determining the carbon particulate concentration of dieselexhaust or other sampled gas which includes filtering diesel exhaust orother sampled gas to separate and collect carbon particulate on a highefficiency filter, measuring the amount of exhaust or sampled gasfiltered, exposing the filtered particulate to oxygen, heating thefiltered particulate to oxidize carbon and form carbon dioxide,measuring the level of the resultant carbon dioxide to arrive at a levelof carbon therein, and calculating the particulate concentration bycomparing the level of carbon with the amount of exhaust or sampled gasmeasured.

The method may also include removing residual carbon dioxide gas fromwithin the oxidizing environment prior to oxidation. The method may alsoinclude heating the filtered particulate incrementally to eliminatevolatile components within the particulate prior to oxidation of thenon-volatile carbon, and may further comprise calculating the volatileand/or non-volatile carbon particulate components.

In a further aspect, the invention involves apparatus for determiningthe carbon particulate level or concentration of diesel exhaust or othersampled gas. The apparatus comprises a means for containing a filter forcollecting carbon particulate from diesel exhaust or other sampled gas,means for removing residual carbon dioxide from within the means forreceiving the filter, means for supplying oxygen within the means forreceiving the filter, means for heating the filter to oxidize carboncollected by the filter, and means for measuring the amount of carbondioxide produced from the oxidation of carbon. The apparatus may alsocomprise a filter for collecting carbon particulate from diesel exhaustor other sampled gas and a means for measuring the amount of dieselexhaust or other sampled gas directed through the filter. The apparatusmay further comprise a means for heating the filter incrementally toseparate volatile from non-volatile components of the filteredparticulate. The apparatus may also include means to oxidize suchvolatile particulate components to facilitate a separate measurement ofthe volatile carbon components, and means for converting any CO producedby partial oxidation into CO₂.

A means for directing diesel exhaust through the filter may be includedwhich comprises a diesel exhaust inlet mountable in fluid flowrelationship between the filter and an exhaust pipe of the dieselengine. The means for supplying oxygen may comprise a valve meanscapable of directing air or other oxygen containing gas into the meansfor receiving the filter. The apparatus may further comprise valve meansfor preventing gas exiting the means for receiving a filter fromentering the means for measuring the carbon dioxide or the means formeasuring the amount of diesel exhaust or other sampled gas directedthrough the filter, and a valve means for preventing diesel exhaust orother sampled gas from flowing through the filter. The apparatus mayfurther comprise a piping system interconnecting the means for receivingthe filter, the means for oxidizing volatile particulate components, andthe means for measuring the amount of carbon dioxide produced from theoxidation of carbon, in a closed loop. Pump means, pressure regulatormeans and/or flow regulator means may advantageously be incorporated inthe closed loop. A section of the piping system connecting the means forcontaining the filter and the means for oxidizing volatile particulatecomponents is preferably heated to prevent volatile components fromcondensing therein. The filter is preferably high temperature resistantto allow reuse and may be comprised of either a ceramic type trap orquartz fiber filter. The means for measuring the carbon dioxide maycomprise an infrared absorption analyzer. The means for measuring theamount of filtered diesel exhaust or other sampled gas may comprise aflowmeter, or a flow controller.

The filter may be built into the apparatus and the whole apparatusconnected to an exhaust pipe or outlet of a diesel engine or vehicleunder test. Alternatively, a separate sampling unit containing thefilter and a means for measuring the amount of diesel gas passingthrough the filter can be connected to the exhaust pipe. After sampling,the particulate laden filter can be removed from the sampling unit andplaced in a separate structure for oxidation of the particulate andmeasurement of resulting carbon dioxide.

In another aspect of the invention, the operation of the apparatus canbe automated and a microcomputer or the like can be used to calculatethe particulate concentration from the measurements of CO₂ and filtereddiesel exhaust or other sampled gas.

In a further aspect of the invention, the amount of different species ofvolatile particulate components may be determined by correlating CO₂measurements with filter heating temperatures.

According to another aspect of the invention, rather than using afilter, carbon particulate can be collected by passing the dieselexhaust or other sampled gas through an accelerating impaction nozzleand impacting carbon particulate on a heatable impaction plate.

In yet another aspect of the present invention, a preseparator can belocated upstream of the filter or other fine particulate collector toremove particulate from the gas stream and/or capture larger sizeparticulate and thereby reduce clogging and extend the useful life ofthe filter or other fine particulate collector. The preseparator mayinclude a heater to facilitate oxidation, measurement and thermalanalysis of carbon particulate captured therein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features, aspects and advantages of the presentinvention will be readily understood from the following detaileddescription, when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 depicts a first embodiment of the apparatus of the presentinvention employing a high efficiency filter and useful in sampling andin measuring the particulate concentration of diesel exhaust or othersampled gas;

FIG. 2 illustrates another embodiment of the apparatus of the presentinvention for receiving a particulate laden filter and measuringparticulate concentration of diesel exhaust or other sampled gas;

FIG. 3 illustrates an embodiment of the present invention employing animpaction nozzle and a heatable impaction plate within an impactionchamber used to collect carbon particulate;

FIG. 3A illustrates further details of the impaction chamber equipmentof FIG. 3;

FIG. 4 presents an illustrative particulate heating temperature functionand a corresponding CO₂ mass measurement profile useful in explaininghow volatile and non-volatile particulate components can be measured;

FIG. 5 illustrates an embodiment of the present invention employing apreseperator;

FIG. 6 depicts an impactor type preseparator;

FIG. 7 depicts a cyclone type presepaparator; and

FIG. 8 depicts a depth filter type preseperator.

In the drawings, like reference numbers are used to identify like parts.

DETAILED DESCRIPTION

A first embodiment of apparatus for determining the particulateconcentration of diesel exhaust, in accordance with the principles ofthe present invention, is shown in FIG. 1. The nature, function andinterconnection of the components of the system will now be described,followed by a full description of the operation of the apparatus.

The apparatus 10 contains an inlet 12 which may be connected to theoutlet end of an exhaust pipe of a diesel engine or diesel poweredvehicle (not shown) thereby enabling the exhaust to flow through theinlet 12 and into the particulate concentration measuring system. Theinlet 12 may be attached directly to the diesel exhaust pipe, or aflexible tubing or duct may be used to place inlet 12 in fluid flowrelationship with the diesel exhaust pipe.

The inlet 12 is connected by a conduit passageway 14 to a chamber 16capable of holding a filter 18 therein. A discharge nipple 20 with avalve 22 therein is located at a point between the inlet 12 and chamber16. When the valve 22 is opened, diesel exhaust which flows through theinlet 12 will be allowed to flow through the discharge nipple 20 and outof the system. A valve 24 is located in the passageway 14 at a pointdownstream from the valve 22. When the valve 24 is opened, exhaust isallowed to flow towards the chamber 16. When the valve 24 is closed,however, exhaust is prevented from flowing towards the chamber 16 andany gas within the chamber 16 is prevented from flowing towards thevalve 22 or inlet 12. A supply tube or nipple 26 is connected to thepassageway 14 downstream from the valve 24 and upstream from the chamber16. The supply nipple 26 has a valve 28 connected thereto and isconnected to an oxygen rich purge gas supply. When the valve 28 isopened and the valve 24 is closed, oxygen rich purge gas is allowed toflow into and within the chamber 16.

The filter chamber 16 contains a filter 18 which is capable of filteringdiesel particulate from diesel exhaust with high efficiency (hereinaftersometimes referred to as a fine particulate filter or a high efficiencyfilter). Preferably, a high temperature resistant filter, such as aquartz fiber, or ceramic trap type, is employed, allowing for filterreuse. The filter 18 is mounted within the chamber 16 in such a fashionas to prevent exhaust gases from flowing through the chamber withoutflowing through the filter 18. A means for heating the chamber iscontained within the system. The heating means may be in the form of aheating coil 19 surrounding the chamber 16 or alternatively may comprisea heating element or heating coil (not shown) within the chamber 16.

Chamber 16 is connected via a piping system 30 in fluid flowrelationship and in a closed loop configuration with a seriesarrangement of oxidizer 32, pump 34, pressure regulator 36, carbondioxide meter 38, flow regulator 40 and valve 42. During a measurementcycle, gases exiting chamber 16 are continuously circulated through thisclosed loop configuration.

Oxidizer 32 may comprise a simple heater such as a glowing nichromewire, or heated platinum or nickel tubing, or may be a conventionalcatalytic converter available in the automotive industry. Oxidizer 32can be advantageously employed to oxidize volatile particulatecomponents, as well as to convert into carbon dioxide any carbonmonoxide produced in chamber 16. These functions are more fullydescribed hereinafter.

Pump 34 located downstream from oxidizer 32 serves to pump gases throughthe piping system 30. Pump 34 is preferably a unidirectional, internallysealed, closed circuit pump.

Gases output from pump 34 flow through pressure regulator 36 into CO₂meter 38. Meter 38 can take many different forms but preferably is of aninfrared absorption analyzer type. Such analyzers are commerciallyavailable in industrially hardened form. Pressure regulator 36 serves toreduce the pressure of gases entering meter 38 to a standard, e.g.ambient level, in order to maintain a constant pressure in CO₂ meter 38and thereby avoid false indications due to pressure changes.

Flow regulator 40 is employed to maintain a constant flow through theclosed loop configuration. Valve 42 serves to either permit or precludefluid flow between regulator 40 and conduit 14 leading to chamber 16. Anoutlet pipe 44 is connected via valve 46 to piping system 30 betweenregulator 40 and valve 42.

The section 48 of piping system 30 connecting chamber 16 to oxidizer 32includes a valve 50 and is surrounded by a heating coil 52 or otherheating means. Valve 50 serves to control the flow of gases intooxidizer 32 while heater 52 is used to prevent volatile particulatecomponents from condensing within pipe section 48.

A flow controller 54 and an associated vacuum pump 56 are connected viavalve 58 to pipe section 48 at a point intermediate of chamber 16 andvalve 50. Vacuum pump 56 serves to draw diesel exhaust through filter 18in chamber 16 while flow controller 54 provides a measure of the amountof filtered diesel exhaust. Valve 58 provides a means for controllingflow through controller 54 and vacuum pump 56 to an outlet pipe 60.Instead of flow controller 54 and vacuum pump 56 a conventional flowmeter can be used to measure the amount of diesel exhaust passingthrough filter 18. The pressure differential supplied by the dieselexhaust coming out of the engine may be used to drive the flow throughchamber 16 and the flow meter.

An electrical signal representative of the amount of filtered dieselexhaust can be provided by flow controller 54 (or an equivalent flowmeter) to a computer 62. Computer 62 also receives an electrical signalrepresentative of the amount of carbon dioxide measured by meter 38.Computer 62 which can be a microprocessor or PC type computerdetermines, from these readings, the particulate concentration of thediesel exhaust. The particulate concentration can be displayed by anoutput device 64 connected to computer 62. Output device 64 maycomprise, for example, a printer, meter or display device. Computer 62can also be programmed in conventional fashion to control the operationof the valves, heating means and other components of the system inaccordance with a desired schedule.

The system 10 operates to measure the particulate concentration ofdiesel exhaust by trapping diesel exhaust particulate within the filter18 and measuring the volume of the exhaust which flows therethrough.After a sufficient amount of exhaust is filtered, oxygen rich gas isforced into the filter chamber 16 to drive out any exhaust fumes thereinand provide an oxygen rich environment. The oxygen rich gas is also usedto purge the closed loop measurement subsystem and to equalize theenvironment therein. The heating means is then activated to raise thetemperature within the filter chamber to a sufficient level so thatparticulate trapped in filter 18, which particulate is nearly 100%carbon, oxidizes to carbon dioxide. Depending upon the temperaturefunction used to heat the filter chamber, volatile particulatecomponents may be driven off the filter without being oxidized. Oxidizer32 serves to oxidize such volatile components as well as to convert anypartially oxidized carbon in the form of carbon monoxide into carbondioxide. The carbon dioxide is then measured by the carbon dioxide meter38 to arrive at a carbon level. Since the particulate within the exhaustis nearly 100% carbon, a measurement of the amount of carbon within theexhaust yields the amount of particulate. The amount of exhaust measuredto have flowed through the filter 18 is compared to the amount ofparticulate to arrive at a particulate concentration level. Oxidation ofparticulate trapped in the filter also serves to clean the filtersufficiently to allow it to be reused again in the same system.Therefore, there is no need to independently clean or to dispose of thefilter after each sampling.

The system is used to measure the particulate concentration of dieselexhaust by attaching the inlet 12 to an exhaust pipe of a diesel poweredvehicle so that the exhaust flows within the inlet 12. If the dieselengine is operating, the valve 22 should be opened and all other valveswithin the system closed so that the exhaust flows through valve 22 outof the system. To begin a sampling cycle, valve 24 and valve 58 areopened to allow exhaust to flow through the chamber 16 and filter 18, aswell as through the flow controller 54, vacuum pump 56 and the outlet 60of the system. Valve 22 may be closed completely, or partially if thefilter is not capable of handling high exhaust capacity. As the exhaustflows through the filter 18, diesel particulate will be collected withinthe filter while the flow through the filter is measured using flowcontroller 54 or other suitable flowmeter.

After a predetermined period of time (or a predetermined volume or massof exhaust flow through the system), the valve 24 can be closed andvalve 22 opened to prevent exhaust from flowing through the filter andforcing exhaust to flow out the discharge nipple 20. Valve 28 is thenopened to allow oxygen rich gas to flow into the chamber 16 and to forceany residual carbon dioxide within chamber 16 out of the system throughoutlet pipe 60. After an appropriate period of time, valve 58 is closedand valves 50 and 46 are opened to purge the rest of the system (i.e.oxidizer 32, pump 34, pressure regulator 36, meter 38, flow regulator 40and the interconnecting piping system 30) of any CO₂ left from theprevious measurement cycle. The purged CO₂ leaves the system throughoutlet pipe 44. This last step also serves to equalize the environmentin the filter chamber 16 and meter 38.

The oxygen rich gas connected to the supply nipple 26 and used to purgethe system may be air or some other gaseous mixture containing a smallpercent of carbon dioxide in which case the purging process establishesa common background level of CO₂ in the closed loop of the system whichcan be measured by meter 38 and subtracted from subsequent reading tocalculate the amount of diesel particulate. When measuring very minuteamounts of diesel particulate it may be advantageous to use a CO₂ -freegas for purging, such as pure oxygen or a mixture of oxygen andnitrogen. In this case, all CO₂ measured by meter 38 will be the resultof oxidation of particulate.

After a sufficient period of time, any exhaust gas within the systemwill have been purged therefrom and the chamber 16 will be completelyfilled with oxygen rich gas. Valves 46 and 28 can then be closed andvalve 42 opened to isolate the closed loop and prevent any gasescirculating therein from escaping. The heater 19 can then be turned onto facilitate oxidation of the carbon within the filter 18.

In one mode of operation, the particulate on filter 18 can be rapidlysubjected to a high temperature on the order of 700° C. to quickly burnoff all of the particulate, both volatile hydrocarbon components andnon-volatile carbon components. Oxidizer 32 ensures that all of thecarbon in the particulate is converted into CO₂. The carbon dioxidemeter 38 measures the resulting amount of carbon dioxide which isdirectly related to the amount of carbon oxidized. The amount or levelof diesel particulate within the exhaust is substantially equal to theamount of carbon.

By comparing this amount of diesel particulate with the amount ofexhaust measured by flow controller 54, particulate concentration can bedetermined. Computer 62, is connected to flow controller 54 and tocarbon dioxide meter 38 and receives measurement readings therefrom. Theoutput of meter 38 is a measurement of the parts per million of CO₂ inthe recirculating gas stream within the closed measurement loop.Knowledge of the volume of the loop (gained through direct measurementor prior calibration by injection of known amounts of CO₂ into the loop)allows ready calculation of the number of molecules of CO₂ by thecomputer. Each molecule of CO₂ corresponds to an individual atom ofcarbon caught in the filter. From the number of carbon atoms, the massof the carbon can be calculated in known fashion. The mass of the carbonis for all practical purposes equal to the mass of the particulate.Dividing the mass of the particulate by the measured amount of filtereddiesel exhaust provides an accurate measure of particulateconcentration. The computer can thus calculate the particulateconcentration of the diesel exhaust from the measurement readings andprovide an output signal representative of particulate concentration toan output device 64, e.g. a printer, meter or display device. Computer62 can also advantageously be employed to control the operation of thevalves, heating means and other components of the system in accordancewith a desired schedule.

Since the diesel particulate is effectively 100% carbon, completeoxidation of the carbon within the filter cleans the filter entirely andallows it to be reused in the same system to again trap dieselparticulate for oxidation into carbon dioxide. Accordingly, highefficiency filters which are also high temperature resistant can beeffectively reused.

In an alternative embodiment of the system of the present invention, theexhaust particulate can be trapped within the high efficiency filterprior to the filter being placed into a chamber for oxidation. In such asystem, exhaust does not have to flow into the system and themeasurement apparatus need not be connected to a diesel exhaust pipe.The alternative embodiment, shown in FIG. 2, contains a conduit 26connecting the chamber 16' to an oxygen rich gas supply and a valve 28to allow the oxygen rich gas to flow into the chamber 16'. Chamber 16'is constructed to allow ready insertion of a particulate laden filter 18therein.

The filter 18, is first placed within a separate sampling unit (notshown) for allowing exhaust to flow therethrough. In this embodiment,the sampling unit is connected to the exhaust pipe of a diesel enginevehicle and diesel particulate is trapped within the filter while theflow therethrough is being measured. After filtering a sufficient amountof particulate from the exhaust, the filter 18 can then be removed fromthe sampling unit and placed within the chamber 16'. The system is thenused as previously described in the aforementioned embodiment. The valve28 upstream of the chamber can be opened allowing the oxygen rich gas toenter chamber 16' therethrough and valve 46 can be opened while valve 42remains closed in order to purge the measurement loop. Valves 46 and 28are then closed and valve 42 opened to establish the closed looprecirculating gas stream. The means for heating the filter can then beactivated to facilitate oxidation of the carbon in filter 18 into carbondioxide. The carbon dioxide meter 38 determines the amount of carbondioxide within the system. The output of CO₂ meter 38 and a flowmeterreading representative of the amount of filtered diesel exhaust areprocessed by computer 62 to determine the particulate concentration ofthe exhaust.

In a further aspect of the invention applicable to both of thepreviously described embodiments, volatile hydrocarbon components can beseparated from the non-volatile carbon components of the particulatetrapped in the filter. In this refinement, the filter with particulatetrapped therein is heated imcrementally (e.g. with a ramp function or instages) in order to first drive off volatile components which can beoxidized into CO₂ by oxidizer 32 and measured by meter 38 and analyzedseparately before the non-volatile carbon is oxidized.

As schematically illustrated in FIG. 4, the filter chamber can be heatedalong a temperature ramp at a particular rate; the rate depending inpart upon the heat capacity of the filter chamber. As the heat graduallyincreases, volatile hydrocarbon components of the particulate evaporateoff of the filter, without being oxidized in the filter chamber, andenter the circulating gas stream. Oxidizer 32 oxidizes the volatilecomponents converting them to CO₂ which is measured by meter 38. Asshown in the upper portion of FIG. 4, as the temperature in the filterchamber gradually increases other hydrocarbons are released from thefilter, oxidized by oxidizer 32, and the resulting CO₂ measured by meter38. Longer chain hydrocarbons have a lower vapor pressure and thereforeevaporate later, i.e. at a higher temperature. Accordingly, as thetemperature is gradually increased, there is a natural discriminationwith respect to which species of hydrocarbons are released. Thecorresponding CO₂ measurements can therefore be used to provide insightinto characterizing the amounts of various hydrocarbon constituents ofthe exhaust.

In the thermal analysis example illustrated, virtually all of thevolatile particulate constituents have been driven off by the time thetemperature reaches about 400° C. Heating beyond this temperature causesthe non-volatile carbon to oxidize resulting in a substantial increasein measured CO₂. In the range of 700°-800° C., all of the carbon hasbeen burnt off.

The section of piping between the filter chamber and oxidizer 32 ispreferably heated to prevent any condensation of volatile hydrocarbonswithin this piping section.

Referring again to the CO₂ profile of FIG. 4, the top level provides ameasure of the total carbon mass, both volatile and non-volatile, in thesample. The reading before the final plateau indicates the amount ofvolatile carbon components. The difference between the highest readingand the volatile carbon reading provides a measure of the mass of thenon-volatile carbon. In this fashion, a measure of volatile tonon-volatile components of the diesel particulate can be achieved.

Alternatively, two samples could be taken where one is totally oxidizedand the other is heated first to drive off volatile components withoutoxidation and then the residue heated and oxidized. The latter sampleyields a measurement of the non-volatile component which can besubtracted from the measurement of total sample to yield the amount ofthe volatile components.

FIGS. 3 and 3A depict an embodiment of the invention in whichparticulate is collected by impaction from a nozzle onto a heatableimpaction plate, rather than with a filter. The system is identical tothat previously described, except that the filter chamber and filter arereplaced by an impaction chamber 66 containing an impaction nozzle 68and a heatable impaction plate 70. In operation, the diesel exhaust isdirected through acceleration nozzle 68 so that the particulate isimpacted against and sticks to the heatable impaction plate 70. Theparticulate deposits in an impaction area 72 on the plate while the flowof exhaust gas continues around the plate and then out of the impactionchamber. Impaction plate 70 may comprise a small temperature controlledhot plate or a band of material through which a current can be run froma current supply 74 to cause the band to heat up. Once the particulatehas been deposited on impaction plate 70, the measurement process isidentical to that described earlier. One advantage of the impactionplate approach is that it allows the deposited particulate to be heatedmore directly than with a filter chamber. As in the filter examples, thedeposited particulate is totally consumed upon oxidation allowing theimpaction plate to be reused for future measurement cycles.

While direct monitoring of raw diesel exhaust is useful for enginetesting, the method and apparatus of the present invention can be usedin other situations as well. These include applications in which thediesel exhaust is diluted and/or mixed with other particulates(carbonaceous and/or inorganic), as well as for monitoring of gas-bornecarbon particulates of a non-diesel origin. Such applications includethe monitoring of carbon (soot) particulates (diesel or otherwise) inambient air, along highways, or in the workplace. In these examples,diesel particulates are usually of particular concern and they arepresent along with inorganic particulates.

Using the previously described collecting and analyzing apparatus of thepresent invention, all carbon particulates (diesel or otherwise) from asampled gas can be detected. However, when the high efficiency filter orcollector of the present invention is used to trap all particulatesincluding non-burnable inorganic ones, the filter renewal capability maybe impaired in that the inorganic particulates will remain trapped inthe filter (or equivalent collector) and may eventually cause it toclog, thus limiting its useful life.

This situation can be alleviated to a certain degree by providing apreseparator 15 upstream of particulate filter 18 (or other equivalentfine particulate collection means) of the measurement apparatus, asshown in FIG. 5. Preseparator 15 serves to remove particulate from thesampled gas stream and/or to sort particulate by size. Dieselparticulates are small in size (and aerodynamic cross-section), whereasinorganic particulates are usually produced by fracturing and abrasionprocesses which tend to produce larger particles. The preseparatorallows the fine particulate (typically oxidizable diesel particulate) topass through to the fine particulate filter 18 in filter chamber 16,while capturing larger size particulate In this way, the fineparticulate filter (or equivalent collecting means) avoids clogging withinorganic particulate and can realize an extended lifetime beyond whatit would have without a preseparator.

Preseparator 15 can include a heater to facilitate oxidation of anycarbon particulate captured by the preseparator, as well as thermalanalysis thereof, in the manner earlier described. The heater for thepreseparator may comprise a separate oven surrounding the preseparator,or other appropriate heating means. Alternatively, the preseparator canbe positioned within the same heatable chamber as the fine particulatefilter. Thermal application and/or analyses, as earlier described, canbe performed on the preseparator and the fine particle collector eithertogether or separately. This provides a measure of total carbonparticulate level or concentration in the gas (both diesel and other)and allows for volatile and non-volatile component measurements, as wellas providing an extended life for the fine particulate collector.

The preseparator can define a particle size cut such that larger sizeparticles are retained by the preseparator and particles below a certainsize are allowed to pass through the preseparator and into the fineparticulate collection stage. The preseparator can take various forms asillustrated in FIGS. 6-8. In these figures, each of the preseparators isshown with an optional heater 19 so that carbon in particulate caught inthe preseparator can be measured and analyzed as well, if desired. Inall cases, the gas stream enters from the viewer's left and exits to theright.

The preseparator of FIG. 6 comprises a classical impactor. In thisembodiment, a gas stream is accelerated through orifice 80 such thatparticles of a specific size, and larger, impact on impaction plate 82.The particle size cut point for this type of impactor depends upon thegeometry of the orifice 80 and its separation from impaction plate 82.The characteristics and operation of such impactors are well known inthe art. Although a classical impactor is shown in FIG. 6, a virtualimpactor, which those skilled in this art will recognize works onsimilar principles, can be used instead.

FIG. 7 depicts a cyclone type preseparator. In the cyclone preseparator,the gas stream enters tangentially through an opening 84 into acylindrical body 86. The resulting rotating gas stream separatesparticles according to their aerodynamic cross-sections so that fineparticles are withdrawn at the exit 88 located at the center of thecylindrical body.

Another embodiment of a preseparator suitable for use in the presentinvention is shown in FIG. 8. This preseparator employs a depth filter90. The depth filter 90 typically includes less densely packed fibrousmaterial or contains larger openings compared to the fine particulatefilter. Thus, the depth filter traps larger sized particulate and isless prone to clogging than the downstream fine particulate filter. Ifsubjected to heating, the depth filter can be made of quartz fibers orthe like.

Other structures which perform the desired particulate pre-separationfunction may be employed as the preseparator 15. Cascaded or multi-stagepreseparators may also be employed. The remaining apparatus of FIG. 5operates in the manner previously described with regard to theembodiment of FIG. 1 to provide an accurate measurement of carbonparticulate level or concentration (diesel or otherwise) of sampled gas.Depending upon the nature and composition of the sampled gas, theintroduction of a separate oxygen rich gas may be unnecessary to createthe desired oxygen rich environment for oxidation and to purge thesystem. A preseparator may also be advantageously incorporated in otherembodiments of the invention, e.g. the system of FIG. 3.

From the foregoing description, it will be apparent that a new methodand apparatus for determining carbon particulate level or concentrationof diesel exhaust or other sampled gas has been developed which can beadvantageously employed, for example, to quickly and accuratelydetermine whether a diesel powered vehicle is operating within emissionstandards. The measurement instrument can be made as both a researchtool and also as a rugged, relatively inexpensive industrial gradedevice. It can produce particulate measurements in short periods of timewith a minimum of labor requirements. Further, it does not require theuse of a dilution tunnel and is immune to measurement confoundinginfluences of water vapor in the exhaust or sampled gas. The process ofthe invention inherently renews the fine particulate filter or collectorfor future use, thereby avoiding the need to either independently cleanor replace the filter or collector after each measurement cycle.Preseparation of inorganic particulates extends the useful life of thefine particulate filter or collector. Further, the invention issusceptible to wide application and can be advantageously employed tomonitor carbon particulate level or concentration in various gaseousmixtures and samples. Another advantage is the ready susceptibility ofthe invention to automated/computer control. The present invention thusrepresents a significant advance in man's efforts to curb air pollutionand maintain air quality.

Although the invention has been described with respect to theembodiments depicted herein, it is evident that the invention may beincorporated into a variety of different embodiments. All suchembodiments are intended to be within the scope of the invention asdefined by the following claims.

What is claimed is:
 1. A method for determining the level orconcentration of carbon particulate of sampled gas, comprising the stepsof:preseparating certain particulate out of the sampled gas; collectingcarbon particulate from the preseparated sampled gas; exposing thecollected particulate to oxygen; heating the collected particulate tooxidize carbon within the particulate to carbon dioxide; measuring thelevel of resultant carbon dioxide; and providing an indication of thelevel or concentration of carbon particulate based on the measured levelof the resultant carbon dioxide.
 2. The method of claim 1 wherein thecollecting step comprises:collecting carbon particulate from a measuredamount of sampled gas; and wherein said indication providing stepcomprises determining a level of carbon within the collected particulatefrom the measured level of resultant carbon dioxide, and calculatingcarbon particulate concentration by comparing the level of carbon withthe measured amount of sampled gas.
 3. The method of claim 1 wherein thepreseparating step comprises preseparating inorganic particulate out ofthe sampled gas.
 4. The method of claim 1 wherein the preseparating stepcomprises preseparating particulate of a specified size and greater outof the sampled gas.
 5. The method of claim 1 further comprising the stepof heating preseparated particulate to facilitate oxidation of anycarbon contained therein.
 6. The method of claim 1 wherein thecollecting step comprises one of (a) passing the sampled gas through anacceleration nozzle and impacting the carbon particulate upon a heatableimpaction plate, and (b) passing the sampled gas through a highefficiency, high temperature resistant filter.
 7. The method of claim 1wherein the collected carbon particulate is heated incrementally toevaporate volatile components of the particulate prior to oxidation ofnon-volatile carbon of said particulate; and further comprising the stepof oxidizing the evaporated volatile components into carbon dioxide. 8.The method of claim 1 further comprising the step of converting carbonmonoxide which may be produced by partial oxidation of carbon intocarbon dioxide.
 9. The method of claim 1 wherein said sampled gascomprises diesel exhaust; and further comprising the step of purgingresidual carbon dioxide gas from the vicinity of the collected carbonparticulate with an oxygen rich gas prior to oxidation.
 10. Apparatusfor providing an indication of the level or concentration of carbonparticulate collected and retained by collection means from sampled gascomprising:means for containing collection means having collected andretained carbon particulate; means for heating collected particulatewithin said containing means to oxidize carbon of said particulate;means for measuring the amount of carbon dioxide produced from oxidationof the carbon of said particulate; means for establishing a closedrecirculating gas measurement loop incorporating said containing means,a separate oxidizer, a pump and said measuring means; and means forproviding an indication of the level or concentration of carbonparticulate based on the amount of carbon dioxide measured in saidclosed recirculating gas measurement loop.
 11. The apparatus of claim 10wherein the means for providing an indication comprises:computer meansfor calculating particulate concentration from the measured amount ofcarbon dioxide and a measurement of the amount of a sampled gas fromwhich the particulate is collected.
 12. The apparatus of claim 10further comprising:means for directing sampled gas at said collectionmeans within said containing means; and means for measuring an amount ofsampled gas directed at said collection means.
 13. The method of claim 1wherein the measuring step comprises:circulating resultant carbondioxide through a closed measurement loop and measuring the level ofresultant carbon dioxide within said loop.
 14. A method for determiningthe level or concentration of carbon particulate of sampled gas,comprising the steps of:collecting carbon particulate from sampled gasby passing the sampled gas through an acceleration nozzle and impactingthe carbon particulate upon a heatable impaction plate; exposing thecollected particulate to oxygen; heating the collected particulatethrough the heatable impaction plate to oxidize carbon within theparticulate to carbon dioxide; measuring the level of resultant carbondioxide; and providing an indication of the level or concentration ofcarbon particulate based on the measured level of the resultant carbondioxide.
 15. The method of claim 14 wherein the collecting step furthercomprises collecting carbon particulate from a measured amount ofsampled gas; andwherein said indication providing step comprisesdetermining a level of carbon within the collected particulate from themeasured level of resultant carbon dioxide, and calculating carbonparticulate concentration by comparing the level of carbon with themeasured amount of sampled gas.
 16. Apparatus for determining the levelor concentration of carbon particulate of sampled gas comprising:meansfor preseparating certain particulate out of the sampled gas; means forcollecting carbon particulate from the preseparated sampled gas; meansfor exposing the collected particulate to oxygen; means for heating thecollected particulate to oxidize carbon within the particulate to carbondioxide; means for measuring the level of resultant carbon dioxide; andmeans for providing an indication of the level or concentration ofcarbon particulate based on the measured level of the resultant carbondioxide.
 17. The apparatus of claim 16 wherein the preseparating meanscomprises means for preseparating inorganic particulate out of thesampled gas.
 18. The apparatus of claim 16 wherein the preseparatingmeans comprises means for preseparating particulate of a specified sizeand greater out of the sampled gas.
 19. The apparatus of claim 16further comprising means for heating preseparated particulate tofacilitate oxidation of any carbon contained therein.
 20. Apparatus fordetermining the level or concentration of carbon particulate of sampledgas comprising:means for collecting carbon particulate from sampled gas,said collecting means comprising means for accelerating sampled gas flowand for collecting by impaction upon a directly heatable impaction platecarbon particulate from the accelerated sampled gas flow; means forexposing the collected particulate to oxygen; means for heating thecollected particulate through said impaction plate to oxidize carbonwithin the particulate to carbon dioxide; means for measuring the levelof resultant carbon dioxide; and means for providing an indication ofthe level or concentration of carbon particulate based on the measuredlevel of the resultant carbon dioxide.
 21. The apparatus of claim 20wherein said accelerating means comprises an acceleration nozzle andwherein the heating means comprises means for supplying an electricalcurrent to the impaction plate.